The present invention relates to powders and products of tantalum, niobium, and their alloys having low oxygen contents, and processes for producing the same.
The present invention is also a response to the problem of establishing high purity tantalum wire with under 100 PPM of oxygen impurity for use as an effective lead wire for sintered tantalum powder solid electrolytic capacitors. The invention also involves other metals and usage of such other metals and tantalum in applications other than as lead wires.
Other applications of the present invention include the production of aerospace alloys similar to those fabricated by the processes disclosed by Robert W. Balliett et al in their patents U.S. Pat. No. 5,918,104 issued Jun. 29, 1999 and U.S. Pat. No. 5,940,675 issued Aug. 17, 1999.
The present invention also relates to composite materials and methods of manufacturing the same, the composites including Axe2x80x94B combinations where A is selected from the group consisting of refractory metals (Nb, Ta, W, Mo, Zr, Hf, Re) and their alloys with each other and still further materials and B is selected from lower melting metals including Cu, Al, Ni, Mg and alloys thereof.
The present invention also relates to metal sheets bent into non-planar forms to provide an integral cone, cup angle bent or other shape without welded or otherwise joined seams and more particularly to such non planar sheets mode of refractory metalsxe2x80x94Ta, Nb, Ti, Mo, W, Zr, Hf, Rexe2x80x94and more particularly Ta, Nb, including alloys of all the foregoing with each other and/or with other alloying ingredients.
The present invention further relates to sputter deposition coating (sputtering) applying such refractory metals. In sputtering a discharge is created and ions from the discharge bombard a target, often of such refractory metal, and atoms of the metal or even gross particles are pushed off the surface (sputtered) and deposited on a separate substrate. The target may be an electrode participating in forming the discharge and/or accelerating ions to the target surface or may be passive (with other electrodes serving for the discharge/acceleration). Sputter deposition is used in many applications including building up of solid state microelectronic components and integrated circuits, solid state detectors and detector arrays, light emitting diodes and arrays of such.
The invention also relates to usage of such refractory metals (elements, alloys) as containers for high temperature operations, e.g. serving as crucibles or rack mounts or other supports for holding materials to be heated at temperatures above 1,500xc2x0 C., sometimes above 2,000xc2x0 C.
The invention also relates to other forms of such refractory metals which are fabricated into parts that are exposed to high temperature and other adverse service condition usage, such as a leading edge of an airplane or missile wing, fin, nose fairing, propeller blade wall, etc. exposed to one or more of temperature, wind, chemicals, vibration and a variety of static and dynamic loads in service usage.
The present invention also relates to production of large sized metal parts (mill products and fabricated parts) produced by extrusion of pre-formed compacts of metal powder to overcome the batch size limitations of conventional powder metallurgy and more particularly to several applications areas or such extrusion processing.
The invention comprises new powders of tantalum, niobium or alloys of tantalum or niobium having an oxygen content of less than about 300 PPM, preferably below 200 PPM and more preferably below 100 PPM. The invention also comprises a method for producing these powders wherein hydrides of tantalum, niobium or alloy powders are heated in the presence of an oxygen-active metal, such as magnesium.
The present invention comprises mixing of refractory metal powders (one or more of Nb, Ta, Ti, W, Mo, Zr, Hf, Re, preferably Nb or alloys thereof) and lower melting matrix powder (one or more of Cu, Al, Ni, Mg, preferably Cu or alloys thereof) in a mass proportion and selected size ranges and morphology (particularly as the refractory metal) to allow for subsequent mechanical working to a final fibrous or ribbon form.
The powder blend is consolidated and subject to thermomechanical working and can include HIPing, extrusion, hot rolling, swaging, forging and cold work steps such as rolling or wire drawing with or without intermediate or end anneals. The matrix metal is made with low oxygen content to prevent fracture or other breakdown in the course of such working. The oxygen lowering treatment of exposure to alkaline earth (Mg, Ca) and/or hydrogen or hydrogen source (methane, ammonia, hydrides) can be employed.
Preferably the composite combination is a Cuxe2x80x94Nb blend encapsulated in an extrusion can and the thermomechanical working comprises extrusion to effect at least a 5:1, preferably 8:1 extrusion ratio reduction.
The invention also comprises formed powder metal products having oxygen contents less than about 300 PPM, preferably below 200 PPM and more preferably below 100 PPM, formed from tantalum, niobium, and their alloys. Further discovered is a new process for producing formed powder metal products of tantalum, niobium and their alloys, having very low oxygen contents without resistance sintering.
The present invention utilizes a combination and variation of the two lines of very old prior art development outlined above, taken together with the further realization that this is a way to achieve a powder of very fine size with low oxygen usable in mill products/fabricated parts manufacture. Normally the achievement of fine size (and related high surface area) of powder is associated with high oxygen pick-up deleterious to subsequent processing and use.
The object of the invention is achieved as to each of the several application areas (sputtering, crucibles, curved aerodynamically shaped devices, and others) by provision of integrally formed refractory metals of curved sheet forms closed on themselves without use of welds, laps, seams or fasteners in the zone of usage challenge and preferably entirely free of such artifacts. Such shapes may be referred to as pots or seamless pots. They are provided as deep or shallow cups or dish forms, cones (coming to a point or truncated), cylinders or part cylinders or part spheres, corrugated sheets or planar or curved sheets with arrays of curving or conical dimples. The refractory metals may be of elemental or alloy forms and may be free standing or laminated to backup sheets of lower cost or otherwise functional metals (e.g. copper for electrical or thermal conductivity, steel or nickel alloys for structural support, etc.).
One embodiment of the present invention pertains to sputtering targets of refractory metals, and in particular tantalum and tantalum alloys, and methods of their fabrication. These targets are characterized by low oxygen, high density, fine grain-size and extremely high uniformity in all directions, providing heretofore unachievable sputtering performance. The tantalum or tantalum alloy powder is produced according to the method disclosed herein. The powder may be consolidated to a high density by various techniques. The powder may be canned in copper, molybdenum-coated steel or other materials to protect it from contamination as it is consolidated at high temperature. The can may or may not be removed by pickling or machining. The consolidated material may be thermo-mechanically processed to a sputtering target as disclosed herein or by another method. For economic reasons, it is common practice to bond tantalum sputtering targets to copper plates or other substrates. In the case of powder canned in copper and possibly other materials like molybdenum, using the can which bonds to the target during consolidation as the backing plate may eliminate this bonding step.
A further embodiment of the present invention is the process of making wires via a powder metallurgy route using tantalum hydride powders that are packed into a shell. The powders are loosely filled into the shell and then dehydrided in situ while loosely contained in the shell. The shell is then closed in and used as an extrusion billet to produce a rod which can be used directly or subjected to further size reduction by forging, swaging and/or wire drawing or rolling steps to produce a final wire or sheet mill product and/or formed into a final fabricated part at that time or later. Both the extrusion step and later forming step(s) are made more effective by the original steps of provision of loose hydride powders into a container that will become an extrusion billet, dehydriding in situ and immediately sealing up the billet to prevent oxygen absorption and then extruding. After cooling, the extruded product, i.e. the resultant rod, the original can material now constituting a thin surface layer of the rod can be removed. The term xe2x80x9crodxe2x80x9d as used herein includes all sizes of the rod and wire range practically achievable via extrusion as well as all cross-section forms.
It is a principal object of the present invention to provide a method of achieving fine tantalum and/or niobium powder with low oxygen, preferably averaging under 150 micrometer (micron) size and below 300 PPM of oxygen, preferably below 200 PPM and more preferably below 100 PPM.
This is accomplished by providing a fine size of tantalum hydride powder of minus 150 microns and mixing it with a small amount of magnesium or calcium, less than 1/2% of the hydride weight. A precursor of the alkaline earth metal such as a hydride thereof can also be employed. The mixture is heated in a ramping up heating schedule to vaporize the alkaline earth metal and to start reduction of oxygen by the vapor, holding to complete the reaction of oxygen, then cooling, and acid and water washing to leach off residual alkaline earth metal and drying to yield a tantalum powder of low oxygen (typically under 150 PPM) and particle size averaging under 150 microns FAPD (Fisher Average particle Diameter).
An advantage of the powder of the present invention is that it comprises relatively non-spherical particles suited for unidirectional mechanical pressing.
A further advantage of the powder of the present invention is that it comprises relatively small particles well suited for cold isostatic pressing.
An advantage of the formed products of tantalum, niobium or their alloys, of the present invention, is that the products can be of any shape, cross-section or size.
An advantage of the process for producing formed products of the present invention is that the process allows for the production of tantalum, niobium, or alloy formed products having low oxygen content as described above and being of any shape cross-section or size.
In addition to application for Ta, Nb and alloys (Taxe2x80x94Nb), the invention can also be applied to other refractory metals, e.g., Mo, W, Ti, Zr, Hf, Re and alloys of the same with each other and/or Nb or Ta.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which: